Hitachi 42PMA400E power supply

Discussion in 'General Electronics Chat' started by rastaman46, Aug 24, 2014.

  1. rastaman46

    Thread Starter Member

    Nov 17, 2011
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    Hi all
    I got hitachi tv that wont turn on when i press power buton all it does is makes relay clicking noise but wont turn on.

    I diasembled tv and on power unit found 2 diods burned

    [​IMG]

    Can any one tell me is diod can cause it please?

    Thanks




     
  2. rastaman46

    Thread Starter Member

    Nov 17, 2011
    69
    0
    I have removed diods from board mesuared with multimeter and i have 470v on
    Negative to negative and positive to positive
    And reads 0 other way round is that ok 470v?

    Thanks
     
  3. ISB123

    Well-Known Member

    May 21, 2014
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    Replace them with similar ones,and check the other side of PCB to see if traces are damaged.
     
    Last edited: Aug 24, 2014
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  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    It looks like the diodes have been very hot, but are not burned (the PCB is discolored).
    Check the large capacitors for bulging or leakage.

    Does the meter have a diode test function?
    This should read OL (or an other value for open lead) in one direction and about 0.5 to 1 (the voltage for the test current) in the other direction.

    Bertus
     
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  5. ISB123

    Well-Known Member

    May 21, 2014
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    To me it seems that traces are damaged since it looks like the discolored part is following a trace.
     
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  6. rastaman46

    Thread Starter Member

    Nov 17, 2011
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    Its shows ol in one and 471 in other direction

    Traces are fine

    What can couse this problem where i need to start looking

    Thanks
     
  7. ISB123

    Well-Known Member

    May 21, 2014
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    Check the caps like bertus said they generally are cause of problem in PSU.
     
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  8. rastaman46

    Thread Starter Member

    Nov 17, 2011
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    All caps looks like new
    It have fan on supply when i turn tv on fan spins just for split sec then click noise and off again

    Thanks
     
  9. ISB123

    Well-Known Member

    May 21, 2014
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    The click noise is from the relay shutting down the TV.Since you cant get the error code you will probably have to take it to a repair shop or order a new PSU which is like 60€,check the fuse.
    For how long did you have the TV?
     
    Last edited: Aug 24, 2014
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  10. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    It looks like the powersupply goes into protection.
    There must be an overload somewhere.

    Bertus
     
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  11. rastaman46

    Thread Starter Member

    Nov 17, 2011
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    How do i check it or where to start checking?

    Thanks
     
  12. ISB123

    Well-Known Member

    May 21, 2014
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    Last edited: Aug 24, 2014
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  13. rastaman46

    Thread Starter Member

    Nov 17, 2011
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    Checked to that link

    Got 5v to pin 6
    And pin 1 &10 gnd 6 i got no voltage at all

    What else can i check?
    Thanks
     
  14. rastaman46

    Thread Starter Member

    Nov 17, 2011
    69
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    Got tv on some how !!!

    I gonna do some deep investigation to power supply

    Thanks all
     
  15. ISB123

    Well-Known Member

    May 21, 2014
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    Tell us what did you do in case someone has the same problem.
     
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  16. rastaman46

    Thread Starter Member

    Nov 17, 2011
    69
    0
    Gone true pdf u send me

    All was linking to power supply

    Then i just gently moved all parts just in case of cold solder

    Then pluged cable in boom fan did not gon off
    Looked at the screen boom picture

    Now testing in case it go funny again

    At least i know here power unit cause it

    Thanks
     
  17. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    783
    Discolouration of the PCB is not as uncommon as it should be!

    A DMM set to the diode test range should be used to check each diode out of circuit.

    Its more likely that something on the load side of things is shorted and activating the PSU overcurrent shutdown.

    A relay clicking could be the delay circuit for degauss in a CRT TV - the only thing I can think of a relay for in a LCD TV is possibly inrush surge limiting, either way it probably doesn't indicate much about the fault.
     
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  18. ian field

    Distinguished Member

    Oct 27, 2012
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    If those readings are from an analogue meter Ohms range, the 471 is pretty much meaningless.

    Most DMMs have a diode check range that gives the forward volt drop of a diode - the reading gives some clue to what type of diode it is.

    For leakage; you need to reverse the test leads and switch to the highest resistance range - normally any leakage indicates a faulty diode, but Shottky barrier diodes show some leakage as normal - recheck the forward voltage, a SB diode should read possibly as low as 0.2V.
     
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